Optical fiber lasers are desirable for their excellent beam quality, even when operating at high power. The quality of a beam emitted from an optical fiber is frequently quantified using the measure “M2”, which is a measure of how tightly the beam can be focused in free space. A beam with a perfect Gaussian spatial profile has a theoretical M2 value of one. A problem with applying M2 measurements to optical fibers is that large mode area fibers typically support several modes, and M2 can be relatively insensitive to the amount of power in a higher order mode. M2 is even less useful, and potentially confusing, when propagation in a higher order mode (HOM) is intentional, as individual HOMs have inherently high values of M2. Therefore new measurement techniques capable of quantifying the modal content of fibers that support more than one mode are needed.